CN114096606A

CN114096606A - Crosslinked polymer gel, method for producing same, monomer composition, and method for producing crosslinked polymer particles

Info

Publication number: CN114096606A
Application number: CN202080049083.7A
Authority: CN
Inventors: 河原彻
Original assignee: Sumitomo Seika Chemicals Co Ltd
Current assignee: Sumitomo Seika Chemicals Co Ltd
Priority date: 2019-07-05
Filing date: 2020-07-01
Publication date: 2022-02-25
Also published as: JP7554748B2; WO2021006148A1; KR20220031899A; US20220315682A1; JPWO2021006148A1; EP3995515A1; EP3995515A4

Abstract

The present invention provides a method for producing a crosslinked polymer gel, which comprises a step of obtaining a crosslinked polymer gel by polymerizing a monomer composition containing benzaldehyde and at least one (meth) acrylic acid compound selected from the group consisting of (meth) acrylic acid and a salt thereof, wherein the centrifuge holding capacity of crosslinked polymer particles obtained by coarsely crushing, drying and pulverizing the crosslinked polymer gel is 60g/g or more. The present invention also provides a monomer composition for obtaining a crosslinked polymer gel, which contains at least one (meth) acrylic acid compound selected from the group consisting of (meth) acrylic acid and a salt thereof and benzaldehyde, and the centrifuge retention capacity of crosslinked polymer particles obtained by coarsely crushing, drying and pulverizing the crosslinked polymer gel is 60g/g or more.

Description

Crosslinked polymer gel, method for producing same, monomer composition, and method for producing crosslinked polymer particles

Technical Field

The present invention relates to a crosslinked polymer gel and a method for producing the same, a monomer composition, and a method for producing crosslinked polymer particles.

Background

Conventionally, an absorbent article for absorbing a liquid (e.g., urine) mainly containing water has been used which includes an absorbent material containing a water-absorbent resin (see, for example, patent document 1 below). The water-absorbent resin can be obtained, for example, using crosslinked polymer particles obtained by polymerizing at least one (meth) acrylic acid compound selected from the group consisting of (meth) acrylic acid and a salt thereof to obtain a crosslinked polymer gel, and then coarsely crushing, drying, and pulverizing the crosslinked polymer gel.

Documents of the prior art

Patent document

Patent document 1: japanese laid-open patent publication No. H06-345819

Disclosure of Invention

Technical problem to be solved by the invention

When a liquid containing water as a main component is supplied to an absorbent article, if the liquid is not sufficiently absorbed by an absorbent body of the absorbent article, there is a possibility that a surplus of the liquid flows on the surface of the absorbent article and leaks to the outside of the absorbent article. Therefore, the water-absorbent resin constituting the absorbent body is required to have an excellent water retention amount. Further, by using the crosslinked polymer particles having an excellent water-holding capacity, a water-absorbent resin having an excellent water-holding capacity is easily obtained, and for example, the centrifuge holding capacity of the crosslinked polymer particles is preferably 60g/g or more.

When the crosslinked polymer gel for obtaining the crosslinked polymer particles having such a centrifuge holding capacity is subjected to a processing treatment such as coarse crushing, it is preferable to avoid occurrence of troubles in a processing apparatus. For example, as an index of the ease of processing of the crosslinked polymer gel, it is preferable that the gel be easily cut when the crosslinked polymer gel is cut.

An object of one aspect of the present invention is to provide a method for producing a crosslinked polymer gel that can be easily cut. It is another object of the present invention to provide a crosslinked polymer gel which can be easily cut. Another object of the present invention is to provide a monomer composition capable of giving a crosslinked polymer gel which can be easily cut. Another object of the present invention is to provide a method for producing crosslinked polymer particles using the crosslinked polymer gel.

Means for solving the problems

The present invention provides a method for producing a crosslinked polymer gel, comprising a step of obtaining a crosslinked polymer gel by polymerizing a monomer composition containing benzaldehyde and at least one (meth) acrylic acid compound selected from the group consisting of (meth) acrylic acid and a salt thereof, wherein the crosslinked polymer gel is coarsely crushed, dried, and pulverized to obtain crosslinked polymer particles having a centrifuge retention capacity of 60g/g or more.

Another aspect of the present invention provides a monomer composition for obtaining a crosslinked polymer gel, the monomer composition containing at least one (meth) acrylic acid compound selected from the group consisting of (meth) acrylic acid and a salt thereof and benzaldehyde, the crosslinked polymer gel being coarsely pulverized, dried, and pulverized to obtain crosslinked polymer particles, the retention capacity of the centrifuge being 60g/g or more.

According to the method for producing a crosslinked polymer gel and the monomer composition, a crosslinked polymer gel that can be easily cut can be obtained.

Another aspect of the present invention provides a method for producing crosslinked polymer particles, wherein the crosslinked polymer gel obtained by the above-mentioned method for producing a crosslinked polymer gel is coarsely crushed, dried and pulverized to obtain crosslinked polymer particles.

In another aspect, the present invention provides a crosslinked polymer gel having structural units derived from the above monomer composition.

Effects of the invention

One aspect of the present invention can provide a method for producing a crosslinked polymer gel that can be easily cut. Another aspect of the present invention can provide a crosslinked polymer gel that can be easily cut. Another aspect of the present invention can provide a monomer composition that can obtain a crosslinked polymer gel that can be easily cut. Another aspect of the present invention can provide a method for producing crosslinked polymer particles using the crosslinked polymer gel.

Drawings

Fig. 1 is a cross-sectional view showing an example of an absorbent article.

Fig. 2 is a diagram for explaining the experimental contents of the cutting test.

Detailed Description

Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments, and can be carried out by being variously modified within the scope of the gist thereof.

In the present specification, "acrylic acid" and "methacrylic acid" are collectively referred to as "(meth) acrylic acid". "acrylate" and "methacrylate" are also labeled as "(meth) acrylate". "polyethylene glycol" and "ethylene glycol" are collectively referred to as "(poly) ethylene glycol". The same applies to other expressions including "(poly)". In the numerical ranges recited herein as being differentiated, the upper limit or the lower limit of the numerical range in a certain section may be arbitrarily combined with the upper limit or the lower limit of the numerical range in another section. In the numerical ranges described in the present specification, the upper limit value or the lower limit value of the numerical range may be replaced with the values shown in the examples. "Water-soluble" means that the resin exhibits a solubility of 5% by mass or more in water at 25 ℃. The materials exemplified in this specification may be used alone, or two or more of them may be used in combination. The content of each component in the composition refers to the total amount of a plurality of substances present in the composition, when the plurality of substances corresponding to each component is present in the composition, unless otherwise specified. "physiological saline" means a 0.9 mass% aqueous solution of sodium chloride. The "(content of (meth) acrylic acid compound" and the total mass of (meth) acrylic acid compound "mean the total amount of acrylic acid, acrylate salt, methacrylic acid, and methacrylate salt. "ppm" means mass ppm.

The method for producing a crosslinked polymer gel (crosslinked polymer aqueous gel) according to the present embodiment includes a polymerization step of polymerizing a monomer composition containing benzaldehyde and at least one (meth) acrylic acid compound selected from the group consisting of (meth) acrylic acid and a salt thereof to obtain a crosslinked polymer gel. The monomer composition of the present embodiment is used for obtaining a crosslinked polymer gel, and contains at least one (meth) acrylic acid compound selected from the group consisting of (meth) acrylic acid and a salt thereof, and benzaldehyde. The holding capacity of a centrifuge (hereinafter, referred to as "CRC" in some cases) of the crosslinked polymer particles obtained by coarsely crushing, drying and pulverizing the crosslinked polymer gel obtained by the method for producing a crosslinked polymer gel and the monomer composition of the present embodiment is 60g/g or more.

According to the method for producing a crosslinked polymer gel and the monomer composition of the present embodiment, a crosslinked polymer gel that can be easily cut can be obtained. With such a crosslinked polymer gel, the force required to cut the gel can be reduced. Although the reason why the effect of easily cutting the gel is obtained is not clear, the inventors of the present application presume as follows. However, the reason is not limited to the following. That is, in the case where the CRC of the crosslinked polymer particles is 60g/g or more, the polymerization rate is appropriately controlled by the presence of benzaldehyde at the time of polymerization of the monomer composition containing the (meth) acrylic acid compound, and therefore, the force required for cutting the gel can be reduced.

The crosslinked polymer gel of the present embodiment can be obtained by the method for producing a crosslinked polymer gel of the present embodiment and the monomer composition. The crosslinked polymer gel of the present embodiment has a structural unit derived from the monomer composition of the present embodiment.

CRC of crosslinked polymer particles is short for Centrifuge Retention Capacity. CRC of the crosslinked polymer particles can be measured by the method described in examples described later with reference to EDANA method (NWSP 241.0.R2(15), pages 769 to 778), and specifically can be obtained as a water absorption rate when a nonwoven fabric bag containing 0.2g of the crosslinked polymer particles in a dry state is immersed in 1000g of physiological saline for 30 minutes, and then centrifuged with a centrifuge to dehydrate the bag. As CRC of the crosslinked polymer particles, the measurement at room temperature (25. + -. 1 ℃ C.) can be used.

The CRC of the crosslinked polymer particles is 60g/g or more. The CRC of the crosslinked polymer particles may be 65g/g or more, 70g/g or more, 75g/g or more, 78g/g or more, 80g/g or more, 82g/g or more, 84g/g or more, 85g/g or more, or 86g/g or more. The CRC of the crosslinked polymer particles may be 100g/g or less, 95g/g or less, 90g/g or less, or 87g/g or less. From these viewpoints, the CRC of the crosslinked polymer particles may be 60 to 100 g/g. The crosslinked polymer particles having a CRC of 60g/g or more are crosslinked polymer particles obtained by coarsely crushing, drying and pulverizing a crosslinked polymer gel, and may be crosslinked polymer particles obtained by classifying after pulverization as needed, or particles having a particle diameter of 180 to 850 μm. Coarse crushing can be used, for example, with 40 pores/36.30 cm²Has a discharge port with a circular hole of 6.4mm in diameter. Drying can be carried out, for example, at 180 ℃ for 30 minutes. The pulverization can be carried out, for example, under conditions where the sieve has a trapezoidal hole of 1 mm. The shape of the crosslinked polymer particles may be, for example, a crushed shape or a granular shape.

The crosslinked polymer gel and the crosslinked polymer particles of the present embodiment can include, for example, a crosslinked polymer obtained by polymerizing the monomer composition of the present embodiment. The crosslinked polymer gel and the crosslinked polymer particles of the present embodiment may further contain other components such as a gel stabilizer, a metal chelating agent (ethylenediaminetetraacetic acid and salts thereof, diethylenetriaminepentaacetic acid and salts thereof (e.g., diethylenetriaminepentaacetic acid pentasodium), and the like), a fluidity improver (lubricant), and the like. Other components can be disposed within, on the surface of, or both of the crosslinked polymer.

The crosslinked polymer gel and the crosslinked polymer particles may comprise inorganic particles disposed on the surface of the crosslinked polymer. For example, by mixing a crosslinked polymer and inorganic particles, the inorganic particles can be disposed on the surface of the crosslinked polymer. Examples of the inorganic particles include silica particles such as amorphous silica.

The monomer composition of the present embodiment may contain water, an organic solvent, and the like. The monomer composition of the present embodiment may be an aqueous monomer solution. Examples of the method of polymerizing the monomer composition include aqueous solution polymerization, bulk polymerization, and precipitation polymerization. Among them, the aqueous solution polymerization method is preferable in view of easy acquisition of good water absorption performance (for example, CRC) and easy control of the polymerization reaction. Hereinafter, a case of using an aqueous solution polymerization method will be described as an example of the polymerization method.

The monomer composition of the present embodiment contains at least one (meth) acrylic acid compound selected from the group consisting of (meth) acrylic acid and a salt thereof, and benzaldehyde. The monomer composition of the present embodiment may contain both (meth) acrylic acid and a salt of (meth) acrylic acid. Examples of the salt of (meth) acrylic acid include alkali metal salts (e.g., sodium salt and potassium salt), alkaline earth metal salts (e.g., calcium salt), and the like.

The monomer composition may contain an ethylenically unsaturated monomer different from the (meth) acrylic compound. As the ethylenically unsaturated monomer, a water-soluble ethylenically unsaturated monomer can be used. Examples of the ethylenically unsaturated monomer different from the (meth) acrylic compound include carboxylic acid monomers such as α, β -unsaturated carboxylic acids and salts thereof, e.g., maleic acid, maleic anhydride, and fumaric acid; nonionic monomers such as (meth) acrylamide, N-dimethyl (meth) acrylamide, 2-hydroxyethyl (meth) acrylate, N-hydroxymethyl (meth) acrylamide, and polyethylene glycol mono (meth) acrylate; amino group-containing unsaturated monomers such as N, N-diethylaminoethyl (meth) acrylate, N-diethylaminopropyl (meth) acrylate, and diethylaminopropyl (meth) acrylamide, and quaternary ammonium compounds thereof; sulfonic acid monomers such as vinylsulfonic acid, styrenesulfonic acid, 2- (meth) acrylamido-2-methylpropanesulfonic acid, 2- (meth) acryloylethanesulfonic acid, and salts thereof.

For ethylenically unsaturated monomers having acid groups (e.g., (meth) acrylic acid), the acid groups may be neutralized beforehand by a basic neutralizing agent. Examples of the alkaline neutralizing agent include alkali metal salts such as sodium hydroxide, sodium carbonate, sodium hydrogencarbonate, potassium hydroxide and potassium carbonate; ammonia, and the like. For the purpose of simplifying the neutralization operation, the basic neutralizing agent may be used in the form of an aqueous solution. The neutralization of the acid groups may be carried out before the polymerization of the ethylenically unsaturated monomer as a raw material, or may be carried out during or after the polymerization.

The degree of neutralization of the ethylenically unsaturated monomer by the basic neutralizing agent is preferably 10 to 100 mol%, 30 to 90 mol%, 40 to 85 mol%, or 50 to 80 mol%, from the viewpoint of easily obtaining a good water absorbing performance (for example, CRC) by increasing the osmotic pressure and from the viewpoint of suppressing the occurrence of defects due to the presence of an excess basic neutralizing agent. The "degree of neutralization" is set to a degree of neutralization with respect to all acid groups which the ethylenically unsaturated monomer has.

The content of the (meth) acrylic acid compound is preferably in the following range based on the total mass of the monomer composition. The content of the (meth) acrylic acid compound is preferably 10% by mass or more, 15% by mass or more, 20% by mass or more, 25% by mass or more, 30% by mass or more, or 35% by mass or more from the viewpoint of easy availability of a gel that can be easily cut and easy improvement of CRC. The content of the (meth) acrylic acid compound is preferably 60% by mass or less, 55% by mass or less, 50% by mass or less, less than 50% by mass, 45% by mass or less, or 40% by mass or less, from the viewpoint of easy availability of a gel that can be easily cut and easy improvement of CRC. From these viewpoints, the content of the (meth) acrylic acid compound is preferably 10 to 60% by mass. In the crosslinked polymer particles of the present embodiment, the content of the structural unit derived from the (meth) acrylic compound is preferably in each of the above-mentioned ranges in relation to the content of the (meth) acrylic compound, based on the total mass of the crosslinked polymer particles.

The content of the (meth) acrylic compound is preferably in the following range based on the total amount of the monomers contained in the monomer composition and/or the total amount of the ethylenically unsaturated monomers contained in the monomer composition. The content of the (meth) acrylic acid compound is preferably 50 mol% or more, 70 mol% or more, 90 mol% or more, 95 mol% or more, 97 mol% or more, or 99 mol% or more. The monomer contained in the monomer composition and/or the ethylenically unsaturated monomer contained in the monomer composition may consist essentially of a (meth) acrylic compound (100 mol% of the monomer contained in the monomer composition and/or the ethylenically unsaturated monomer contained in the monomer composition is the (meth) acrylic compound).

The benzaldehyde may be contained in the (meth) acrylic acid compound, or may constitute a monomer composition independently of the (meth) acrylic acid compound.

The content of benzaldehyde is more than 0 mmol, preferably in the following range, relative to 1 mol of the (meth) acrylic acid compound. The content of benzaldehyde is preferably 0.0001 mmol or more, 0.0003 mmol or more, 0.0005 mmol or more, 0.001 mmol or more, 0.0025 mmol or more, 0.003 mmol or more, more than 0.003 mmol, 0.005 mmol or more, 0.01 mmol or more, 0.012 mmol or more, 0.02 mmol or more, 0.03 mmol or more, 0.05 mmol or more, 0.06 mmol or more, 0.08 mmol or more, 0.1 mmol or more, more than 0.1 mmol, 0.2 mmol or more, 0.25 mmol or more, 0.3 mmol or more, more than 0.3 mmol, 0.32 mmol or more, 0.4 mmol or more, 0.45 or more, 0.5 mmol or more, 0.65 mmol or more, 0.6 mmol or more, from the viewpoint of easily obtaining a gel that can be easily cleaved, and easily improving CRC. The content of benzaldehyde is preferably 10 mmol or less, 7 mmol or less, 6 mmol or less, 5 mmol or less, 4 mmol or less, 3 mmol or less, 2.5 mmol or less, 2 mmol or less, 1.5 mmol or less, 1 mmol or less, less than 1 mmol, 0.8 mmol or less, or 0.7 mmol or less, from the viewpoint of easy availability of a gel which can be easily cut, easy improvement of CRC, and easy suppression of the remaining of unreacted monomers. From these viewpoints, the content of benzaldehyde is preferably more than 0 mmol and 10 mmol or less.

The content of benzaldehyde is more than 0ppm, preferably in the following range, based on the total mass of the monomer composition. The content of benzaldehyde is preferably 0.02ppm or more, 0.1ppm or more, 0.15ppm or more, 0.2ppm or more, 0.5ppm or more, 1.0ppm or more, 1.5ppm or more, 2.0ppm or more, 5.0ppm or more, 7.5ppm or more, 12pp or more, 12.5ppm or more, 20ppm or more, 25ppm or more, 30ppm or more, 35ppm or more, 50ppm or more, 60ppm or more, 62.5ppm or more, 75ppm or more, 80ppm or more, 90ppm or more, 100ppm or more, 125ppm or more, 150ppm or more, 175ppm or more, 200ppm or more, 250ppm or more, 300ppm or more, 350ppm or more, or 360ppm or more from the viewpoint of easily obtaining a gel that can be easily cut and from the viewpoint of easily improving CRC. The content of benzaldehyde is preferably 3000ppm or less, 2000ppm or less, 1500ppm or less, 1000ppm or less, 800ppm or less, 600ppm or less, 500ppm or less, 450ppm or less or 400ppm or less from the viewpoint of easy availability of a gel which can be easily cut and easy improvement of CRC. From these viewpoints, the content of benzaldehyde is preferably more than 0ppm and 3000ppm or less.

The monomer composition may contain a polymerization initiator. The polymerization of the monomer contained in the monomer composition can be started by adding a polymerization initiator to the monomer composition and, if necessary, heating, light irradiation, or the like. Examples of the polymerization initiator include a photopolymerization initiator and a radical polymerization initiator, and a water-soluble radical polymerization initiator is preferable. The polymerization initiator preferably contains at least one selected from the group consisting of azo compounds and peroxides, from the viewpoint of easily obtaining a gel that can be easily cleaved and from the viewpoint of easily improving CRC.

Examples of the azo compound include 2, 2' -azobis [2- (N-phenylamidino) propane]Dihydrochloride, 2' -azobis {2- [ N- (4-chlorophenyl) amidino group]Propane dihydrochloride, 2' -azobis {2- [ N- (4-hydroxyphenyl) amidino group]Propane } dihydrochloride, 2' -azobis [2- (N-benzylamidino) propane]Dihydrochloride, 2' -azobis [2- (N-allylamidino) propane]Dihydrochloride, 2 '-azobis (2-amidinopropane) dihydrochloride, 2'-azobis {2- [ N- (2-hydroxyethyl) amidino group]Propane } dihydrochloride, 2' -azobis [2- (5-methyl-2-imidazolin-2-yl) propane]Dihydrochloride, 2' -azobis [2- (2-imidazolin-2-yl) propane]Dihydrochloride, 2' -azobis [2- (4,5,6, 7-tetrahydro-1H-1, 3-diaza ]

-2-yl) propane]Dihydrochloride salt, 2' -azobis [2- (5-hydroxy-3, 4,5, 6-tetrahydropyrimidin-2-yl) propane]Dihydrochloride, 2' -azobis {2- [1- (2-hydroxyethyl) -2-imidazolin-2-yl]Propane } dihydrochloride, 2' -azobis [2- (2-imidazolin-2-yl) propane]Disulfate dihydrate, 2' -azobis [ N- (2-carboxyethyl) -2-methylpropionamidine]Tetrahydrate, 2' -azobis [ 2-methyl-N- (2-hydroxyethyl) propionamide]And the like. The azo compound is preferably selected from the group consisting of 2,2 ' -azobis (2-methylpropionamide) dihydrochloride, 2 ' -azobis (2-amidinopropane) dihydrochloride, and 2,2 ' -azobis {2- [1- (2-hydroxyethyl) -2-imidazolin-2-yl) in terms of easy availability of a gel that can be easily cut and easy availability of good water absorption performance (e.g., CRC)]Propane dihydrochloride and 2, 2' -azobis [ N- (2-carboxyethyl) -2-methylpropionamidine]At least one member of the group consisting of tetrahydrate.

Examples of the peroxide include persulfates such as potassium persulfate, ammonium persulfate, and sodium persulfate; and organic peroxides such as methyl ethyl ketone peroxide, methyl isobutyl ketone peroxide, di-t-butyl peroxide, t-butylcumyl peroxide, t-butyl peroxyacetate, t-butyl peroxyisobutyrate, t-butyl peroxypivalate, and the like. The peroxide preferably contains at least one selected from the group consisting of potassium persulfate, ammonium persulfate, and sodium persulfate, from the viewpoint of easily obtaining a gel that can be easily cut and from the viewpoint of easily obtaining good water absorption performance (e.g., CRC).

The content of the polymerization initiator is preferably in the following range with respect to 1 mole of the (meth) acrylic compound. The content of the polymerization initiator is preferably 0.001 mmol or more, 0.003 mmol or more, 0.015 mmol or more, 0.03 mmol or more, 0.06 mmol or more, 0.08 mmol or more, or 0.1 mmol or more in view of easy availability of a gel which can be easily cleaved, easy improvement of CRC, and reduction of the polymerization reaction time. The content of the polymerization initiator is preferably 5 mmol or less, 4 mmol or less, 2 mmol or less, 1 mmol or less, 0.5 mmol or less, 0.3 mmol or less, 0.25 mmol or less, 0.2 mmol or less, or 0.15 mmol or less from the viewpoint of easy availability of a gel which can be easily cut, easy improvement of CRC, and easy avoidance of a rapid polymerization reaction. From these viewpoints, the content of the polymerization initiator is preferably 0.001 to 5 mmol.

The monomer composition may contain a reducing agent. Examples of the reducing agent include sodium sulfite, sodium hydrogen sulfite, ferrous sulfate, and L-ascorbic acid. The polymerization initiator and the reducing agent may be used simultaneously.

The monomer composition may contain an oxidizing agent. Examples of the oxidizing agent include hydrogen peroxide, sodium perborate, perphosphoric acid and its salts, and potassium permanganate.

The monomer composition may contain an internal crosslinking agent. By using the internal crosslinking agent, the obtained crosslinked polymer can have a crosslinked structure based on the internal crosslinking agent as its internal crosslinked structure in addition to a self-crosslinked structure based on the polymerization reaction.

Examples of the internal crosslinking agent include compounds having 2 or more reactive functional groups (for example, polymerizable unsaturated groups). Examples of the internal crosslinking agent include di-or tri (meth) acrylates of polyhydric alcohols such as (poly) ethylene glycol, (poly) propylene glycol, trimethylolpropane, glycerin, polyoxyethylene glycol, polyoxypropylene glycol, and (poly) glycerin; unsaturated polyesters obtained by reacting the above-mentioned polyhydric alcohol with an unsaturated acid (maleic acid, fumaric acid, etc.); glycidyl group-containing compounds such as (poly) ethylene glycol diglycidyl ether, (poly) propylene glycol diglycidyl ether, (poly) glycerol diglycidyl ether, and glycidyl (meth) acrylate; bisacrylamides such as N, N' -methylenebis (meth) acrylamide; di-or tri (meth) acrylates obtained by reacting polyepoxides with (meth) acrylic acid; carbamyl di (meth) acrylates obtained by reacting a polyisocyanate (toluene diisocyanate, hexamethylene diisocyanate, etc.) with hydroxyethyl (meth) acrylate; an allylated starch; allylated cellulose; diallyl phthalate; n, N', N "-triallyl isocyanurate; divinylbenzene; pentaerythritol; ethylene diamine; polyethyleneimine, and the like. The internal crosslinking agent preferably contains at least one selected from the group consisting of (poly) ethylene glycol diglycidyl ether, (poly) propylene glycol diglycidyl ether, and (poly) glycerol diglycidyl ether, from the viewpoint of easy availability of a gel that can be easily cleaved, easy improvement of CRC, and excellent reactivity at low temperatures.

The content of the internal crosslinking agent is preferably in the following range with respect to 1 mole of the (meth) acrylic compound. The content of the internal crosslinking agent is preferably 0.0005 mmol or more, 0.001 mmol or more, 0.002 mmol or more, 0.005 mmol or more, 0.01 mmol or more, 0.015 mmol or more, 0.02 mmol or more, or 0.025 mmol or more from the viewpoint of easy availability of a gel that can be easily cut and easy availability of good water absorption performance (e.g., CRC). The content of the internal crosslinking agent is preferably 0.3 mmol or less, 0.25 mmol or less, 0.2 mmol or less, 0.18 mmol or less, less than 0.18 mmol, 0.17 mmol or less, 0.16 mmol or less, 0.15 mmol or less, 0.1 mmol or less, 0.06 mmol or less, less than 0.06 mmol, 0.05 mmol or less, less than 0.05 mmol, 0.04 mmol or less, or 0.03 mmol or less, from the viewpoint of easy availability of a gel which can be easily cut and easy availability of good water absorption performance (e.g., CRC). From these viewpoints, the content of the internal crosslinking agent is preferably 0.0005 to 0.3 mmol.

The monomer composition may contain additives such as a chain transfer agent, a thickener, and an inorganic filler as components different from the above components, as required. Examples of the chain transfer agent include thiols, mercaptans, secondary alcohols, hypophosphorous acid, phosphorous acid, and acrolein. Examples of the thickener include carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, methyl cellulose, polyethylene glycol, polyacrylic acid, a neutralized product of polyacrylic acid, and polyacrylamide. Examples of the inorganic filler include metal oxides, ceramics, and viscous minerals.

Examples of the polymerization method of the aqueous solution polymerization include a static polymerization method in which the polymerization is performed in a state where the monomer composition is not stirred (for example, in a static state); a stirring polymerization system in which the monomer composition is polymerized while being stirred in the reaction apparatus. In the standing polymerization mode, at the end of the polymerization, a single block gel having an occupation volume approximately equal to that of the monomer composition once present in the reaction vessel can be obtained.

The polymerization form may be batchwise, semi-continuous, and the like. For example, in the case of a standing polymerization system by continuous polymerization, a gel can be obtained continuously by performing a polymerization reaction while continuously supplying a monomer composition to a continuous polymerization apparatus.

The polymerization temperature varies depending on the polymerization initiator used, but is preferably 0 to 130 ℃ or 10 to 110 ℃ from the viewpoints of improving productivity by shortening the polymerization time by rapidly carrying out polymerization and easily removing the heat of polymerization to smoothly carry out the reaction. The polymerization time may be suitably set in accordance with the kind and amount of the polymerization initiator used, the reaction temperature, and the like, and is preferably 1 to 200 minutes or 5 to 100 minutes.

In the method for producing crosslinked polymer particles according to the present embodiment, the crosslinked polymer gel obtained by the method for producing a crosslinked polymer gel according to the present embodiment is coarsely crushed, dried, and pulverized to obtain crosslinked polymer particles. That is, the method for producing crosslinked polymer particles according to the present embodiment may include: a gel preparation step of obtaining a crosslinked polymer gel by the method for producing a crosslinked polymer gel according to the present embodiment; a gel coarse crushing step of coarsely crushing the crosslinked polymer gel to obtain a coarse crushed material (gel coarse crushed material); a drying step of drying the coarsely pulverized product to obtain a dried product; and a dry-pulverization step of pulverizing the dried product.

As the coarse crushing device in the gel coarse crushing step, for example, a kneader (pressure kneader, double arm kneader, or the like), a meat grinder, a chopper, a medicinal mill (ファーマミル), or the like can be used.

In the drying step, a dried product (gel-dried product) can be obtained by removing a liquid component (water or the like) in the coarsely crushed product by heating and/or blowing air. The drying method may be natural drying, heat drying, spray drying, freeze drying, etc. The drying temperature is, for example, 70 to 250 ℃.

As the pulverizer in the pulverizing step, a roll mill (roll crusher), a pounder, a jet mill, a high-speed rotary pulverizer (hammer mill, pin mill, rotary impact mill, etc.), a container drive mill (rotary mill, vibration mill, planetary mill, etc.), and the like can be exemplified.

The method for producing crosslinked polymer particles according to the present embodiment may include a classification step of classifying the pulverized product (pulverized product of dried product) after the dried product pulverization step. In the classification step, the pulverized material can be classified into 2 or more particle groups having different particle size distributions. In the method for producing crosslinked polymer particles according to the present embodiment, the classification step may be performed a plurality of times by repeating the dry pulverizing step and the classification step, or may be performed after the additional crosslinking step described later. Examples of the classification method include sieve classification and air classification. Examples of the sieve classification include a vibrating sieve, a rotary sieve (rotary sifter), a cylindrical stirring sieve, a blower sieve (wind sifter), and a Ro-Tap type vibrating sieve. The sieve classification is a method of classifying particles on a sieve into particles passing through a mesh of the sieve and particles not passing through the mesh of the sieve by a vibrating sieve. Air classification is a method of classifying particles using the flow of air.

The water-absorbent resin of the present embodiment can be obtained by additionally crosslinking the polymer after the gel crushing step. The additional crosslinking may be performed at any time after the gel coarse crushing step, and may be performed at any time before or after the drying step, before or after the crushing step, or before or after the classification step. The additional crosslinking may be surface crosslinking of the polymer particles. The additional crosslinking can be performed, for example, by reacting a crosslinking agent (e.g., a surface crosslinking agent) with the polymer. By performing additional crosslinking using a crosslinking agent, the crosslinking density of the polymer (for example, the crosslinking density in the vicinity of the surface of the polymer particle) is increased, and therefore the water absorption performance (CRC, water absorption under load, water absorption rate, etc.) of the polymer is easily improved.

Examples of the crosslinking agent include compounds having 2 or more functional groups (reactive functional groups) reactive with functional groups derived from the ethylenically unsaturated monomer. Examples of the crosslinking agent include polyhydric alcohols such as ethylene glycol, propylene glycol, 1, 4-butanediol, trimethylolpropane, glycerin, polyoxyethylene glycol, polyoxypropylene glycol, and polyglycerin; polyglycidyl compounds such as (poly) ethylene glycol diglycidyl ether, (poly) glycerol triglycidyl ether, (poly) propylene glycol polyglycidyl ether, and (poly) glycerol polyglycidyl ether; halogenated epoxy compounds such as epichlorohydrin, epibromohydrin, and α -methyl epichlorohydrin; compounds having 2 or more reactive functional groups such as isocyanate compounds (2, 4-tolylene diisocyanate, hexamethylene diisocyanate, etc.); oxetane compounds such as 3-methyl-3-oxetanemethanol, 3-ethyl-3-oxetanemethanol, 3-butyl-3-oxetanemethanol, 3-methyl-3-oxetaneethanol, 3-ethyl-3-oxetaneethanol and 3-butyl-3-oxetaneethanol; oxazoline compounds such as 1, 2-ethylenebisoxazoline; carbonate compounds such as ethylene carbonate; hydroxyalkyl amide compounds such as bis [ N, N-di (. beta. -hydroxyethyl) ] hexanediamide, and the like.

The water-absorbent resin of the present embodiment may contain a gel stabilizer on the surface thereof; metal chelating agents (ethylenediaminetetraacetic acid and salts thereof, diethylenetriaminepentaacetic acid and salts thereof (e.g., diethylenetriaminepentaacetic acid pentasodium), and the like); inorganic particles of a fluidity improver (lubricant), and the like. For example, the inorganic particles can be disposed on the surface of the polymer by mixing the polymer after additional crosslinking with the inorganic particles. Examples of the inorganic particles include silica particles such as amorphous silica.

The water-absorbent resin of the present embodiment can retain water and absorb body fluids such as urine, sweat, and blood (e.g., menstrual blood). The water-absorbent resin of the present embodiment can be used as a constituent component of an absorbent body. The present embodiment can be used for sanitary materials such as disposable diapers and sanitary products; agricultural and horticultural materials such as water-retaining agents and soil improvers; water-stopping agent, anti-dewing agent and other industrial materials.

The absorbent material of the present embodiment contains the water-absorbent resin (for example, water-absorbent resin particles) of the present embodiment. The absorbent material of the present embodiment may contain a fibrous material, for example, a mixture containing a water-absorbent resin and a fibrous material. The absorbent body may have a structure in which, for example, a water-absorbent resin and fibrous materials are uniformly mixed, a structure in which a water-absorbent resin is sandwiched between fibrous materials formed into a sheet or layer, or other structures.

Examples of the fibrous material include finely pulverized wood pulp; cotton; cotton linters; artificial silk; cellulose fibers such as cellulose acetate; synthetic fibers such as polyamide, polyester, and polyolefin; mixtures of these fibers, and the like. As the fibrous material, hydrophilic fibers can be used.

In order to improve the shape retention of the absorbent body before and during use, the fibers may be bonded to each other by adding an adhesive binder to the fibrous material. Examples of the adhesive binder include heat-fusible synthetic fibers, hot-melt adhesives, and adhesive emulsions.

Examples of the heat-fusible synthetic fibers include all-melt adhesives such as polyethylene, polypropylene, and ethylene-propylene copolymers; and a non-all-melt type adhesive agent having a side-by-side structure or a core-sheath structure of polypropylene and polyethylene. In the above-described non-all-melt adhesive, only the polyethylene part can be thermally welded.

Examples of the hot melt adhesive include a mixture of a base polymer (base polymer) such as an ethylene-vinyl acetate copolymer, a styrene-isoprene-styrene block copolymer, a styrene-butadiene-styrene block copolymer, a styrene-ethylene-butylene-styrene block copolymer, a styrene-ethylene-propylene-styrene block copolymer, or amorphous polypropylene, and a tackifier, a plasticizer, an antioxidant, and the like.

Examples of the adhesive emulsion include a polymer of at least one monomer selected from the group consisting of methyl methacrylate, styrene, acrylonitrile, 2-ethylhexyl acrylate, butyl acrylate, butadiene, ethylene, and vinyl acetate.

The absorber of the present embodiment may contain inorganic powder (e.g., amorphous silica), deodorant, antibacterial agent, pigment, dye, perfume, adhesive, and the like. In the case where the water-absorbent resin contains inorganic particles, the absorber may contain an inorganic powder different from the inorganic particles in the water-absorbent resin.

The shape of the absorbent body of the present embodiment may be, for example, a sheet shape. The thickness of the absorber (for example, the thickness of the sheet-like absorber) may be 0.1 to 20mm or 0.3 to 15 mm.

From the viewpoint of easily obtaining sufficient absorption properties, the content of the water-absorbent resin in the absorbent material may be 2 to 95 mass%, 10 to 80 mass%, or 20 to 60 mass% with respect to the total of the water-absorbent resin and the fibrous material.

The content of the water-absorbent resin in the absorbent material is preferably 1m per unit of the absorbent material, from the viewpoint of easily obtaining sufficient absorption characteristics²The absorbent is 100-1000 g, 150-800 g or 200-700 g. The content of the water-absorbent resin in the absorbent material is preferably 1m per unit of the absorbent material, from the viewpoint of easily obtaining sufficient absorption characteristics²The absorbent is 50-800 g, 100-600 g or 150-500 g.

The absorbent article of the present embodiment includes the absorbent body of the present embodiment. Examples of the other components of the absorbent article of the present embodiment include a core wrap that prevents the components of the absorbent body from falling off and flowing while maintaining the shape of the absorbent body; an outermost liquid-permeable sheet disposed on the liquid-impregnated side of the liquid-absorbing object; an outermost liquid-impermeable sheet disposed on the side opposite to the liquid-impregnated side of the liquid-absorbing object. Examples of absorbent articles include diapers (e.g., disposable diapers), toilet training pants, incontinence pads, sanitary materials (e.g., sanitary napkins and tampons), sweat-absorbent pads, pet pads, toilet components, and animal waste disposal materials.

Fig. 1 is a cross-sectional view showing an example of an absorbent article. The absorbent article 100 shown in fig. 1 includes an absorber 10, a core wrap 20a, a core wrap 20b, a liquid-permeable sheet 30, and a liquid-impermeable sheet 40. In the absorbent article 100, a liquid-impermeable sheet 40, a core wrap 20b, an absorber 10, a core wrap 20a, and a liquid-permeable sheet 30 are stacked in this order. Although there is a portion illustrated in fig. 1 such that there is a gap between the members, the members may be closely fitted without the gap.

The absorbent body 10 has water-absorbent resin particles 10a containing the water-absorbent resin of the present embodiment and a fiber layer 10b containing a fibrous material. The water-absorbent resin particles 10a are dispersed in the fiber layer 10 b.

The core sheet 20a is disposed on one side of the absorbent body 10 (the upper side of the absorbent body 10 in fig. 1) in a state of being in contact with the absorbent body 10. The core sheet 20b is disposed on the other side of the absorbent body 10 (the lower side of the absorbent body 10 in fig. 1) in a state of being in contact with the absorbent body 10. The absorber 10 is disposed between the core wrap 20a and the core wrap 20 b. Examples of the core wrap sheet 20a and the core wrap sheet 20b include a tissue (tissue), a nonwoven fabric, a woven fabric, a synthetic resin film having liquid-permeable holes, and a mesh sheet having meshes. The core sheet 20a and the core sheet 20b have, for example, main surfaces having the same size as the absorber 10.

The liquid-permeable sheet 30 is disposed at the outermost portion on the liquid-impregnated side of the absorption object. The liquid-permeable sheet 30 is disposed on the core wrap sheet 20a in a state of being in contact with the core wrap sheet 20 a. Examples of the liquid-permeable sheet 30 include nonwoven fabrics and porous sheets made of synthetic resins such as polyethylene, polypropylene, polyester, and polyamide. The liquid-impermeable sheet 40 is disposed at the outermost portion of the absorbent article 100 on the side opposite to the liquid-permeable sheet 30. The liquid-impermeable sheet 40 is disposed below the core wrap sheet 20b in a state of being in contact with the core wrap sheet 20 b. Examples of the liquid-impermeable sheet 40 include sheets made of synthetic resins such as polyethylene, polypropylene, and polyvinyl chloride, and sheets made of composite materials of these synthetic resins and nonwoven fabrics. The liquid-permeable sheet 30 and the liquid-impermeable sheet 40 have, for example, main surfaces larger than the main surfaces of the absorber 10, and outer edge portions of the liquid-permeable sheet 30 and the liquid-impermeable sheet 40 extend to the periphery of the absorber 10, the core sheet 20a, and the core sheet 20 b.

The size relationship among the absorber 10, the core wrap 20a, the core wrap 20b, the liquid-permeable sheet 30, and the liquid-impermeable sheet 40 is not particularly limited, and can be appropriately adjusted according to the use of the absorbent article and the like. The method of holding the shape of the absorber 10 using the

core wrap sheets

20a and 20b is not particularly limited, and as shown in fig. 1, the absorber may be wrapped with a plurality of core wrap sheets, or may be wrapped with 1 core wrap sheet.

The absorption body can be glued to the topsheet. In the case where the absorbent body is sandwiched or wrapped by the core wrap sheet, it is preferable that at least the core wrap sheet is bonded to the topsheet, and it is more preferable that the core wrap sheet is bonded to the absorbent body at the same time as the core wrap sheet is bonded to the topsheet. Examples of the method for bonding the absorbent body include: a method of applying a hot-melt adhesive to the top sheet at predetermined intervals in the width direction thereof in a longitudinal stripe shape, a spiral shape, or the like, and bonding the top sheet using a water-soluble adhesive selected from starch, carboxymethyl cellulose, polyvinyl alcohol, polyvinyl pyrrolidone, and other water-soluble polymers. When the absorbent material contains a heat-fusible synthetic fiber, a method of bonding by heat-fusing of the heat-fusible synthetic fiber may be employed.

According to the present embodiment, a liquid-absorbing method using the water-absorbent resin, the absorbent body, or the absorbent article of the present embodiment can be provided. The liquid-absorbing method of the present embodiment includes a step of bringing a liquid to be absorbed into contact with the water-absorbent resin, the absorbent body, or the absorbent article of the present embodiment.

According to the present embodiment, a method for producing an absorbent body using the water-absorbent resin can be provided. The method for producing an absorbent body of the present embodiment includes a water-absorbent resin production step for obtaining the water-absorbent resin. The method for producing an absorbent body according to the present embodiment may include a step of mixing the water-absorbent resin and the fibrous material after the step of producing the water-absorbent resin. According to the present embodiment, a method for manufacturing an absorbent article using the absorbent body obtained by the above-described method for manufacturing an absorbent body can be provided. The method for producing an absorbent article according to the present embodiment includes an absorbent body production step of obtaining an absorbent body by the above-described method for producing an absorbent body. The method of manufacturing an absorbent article according to the present embodiment may include a step of obtaining an absorbent article using the absorbent body and another component of the absorbent article after the absorbent body manufacturing step, and in this step, for example, the absorbent article may be obtained by stacking the absorbent body and another component of the absorbent article on each other.

According to the present embodiment, there can be provided an application of a water-absorbent resin, an absorbent body, and an absorbent article to liquid absorption. According to the present embodiment, there can be provided an application of a crosslinked polymer gel to adjust a force required for cutting the crosslinked polymer gel. According to the present embodiment, it is possible to provide a method of adjusting a force required for cutting a crosslinked polymer gel, in which the force required for cutting the crosslinked polymer gel is adjusted according to the amount of benzaldehyde in a monomer composition for obtaining the crosslinked polymer gel.

Examples

The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

< preparation of gel >

(example 1)

A stirrer (diameter: 8mm, length: 40mm, no ring) was placed in the center of a stainless steel barrel (outer dimension of opening: 210 mm. times.170 mm, inner dimension of bottom: 170. times.130 mm, height: 30mm) having an inner surface coated with a fluororesin. 340.0g of a partially neutralized solution of sodium acrylate (monomer for polymerization, monomer concentration: 45 mass%, neutralization rate of sodium acrylate: 75 mol%), 0.0077g of ethylene glycol diglycidyl ether (internal crosslinking agent, 0.044 mmol), 0.374mg of benzaldehyde (0.0035 mmol) and 59.0g of ion-exchanged water were added, and then the mixture was uniformly mixed by rotating a stirrer to obtain a mixture (concentration of partially neutralized solution of sodium acrylate: 38 mass%). Then, the inside of the stainless steel tub was sealed by sealing the upper portion of the stainless steel tub with a polyethylene film. After the temperature of the mixture in the stainless steel barrel was adjusted to 25 ℃, the dissolved oxygen content was adjusted to 0.1ppm or less by replacing the mixture with nitrogen. Subsequently, 3.09g of a 2 mass% aqueous solution of potassium persulfate (potassium persulfate: 0.229 mmol) and 0.65g of a 0.5 mass% aqueous solution of L-ascorbic acid were successively dropped while stirring at 300rpm, thereby preparing an aqueous monomer solution. Polymerization was started after dropping 0.5 mass% L-ascorbic acid aqueous solution for 2 minutes. 22 minutes after the start of the polymerization, the obtained product was directly placed in a vessel and immersed in a water bath at 75 ℃ for 20 minutes to be aged, thereby obtaining a gel (gel after polymerization). The thickness of the gel was 1.3 cm. The same operation was performed, thereby obtaining two gels, gel a for making crosslinked polymer particles and gel B for performing a cutting test.

(example 2)

A gel was obtained by performing the same operation as in example 1, except that the amount of benzaldehyde used was changed to 1.245mg (0.0117 mmol).

(example 3)

A gel was obtained by performing the same operation as in example 1, except that the amount of benzaldehyde used was changed to 2.490mg (0.0234 mmol).

(example 4)

A gel was obtained by performing the same operation as in example 1, except that the amount of benzaldehyde used was changed to 87.15mg (0.819 mmol).

(example 5)

A gel was obtained by performing the same operation as in example 1, except that the amount of benzaldehyde used was changed to 124.5mg (1.173 mmol).

(example 6)

A gel was obtained by performing the same operation as in example 1, except that the amount of ethylene glycol diglycidyl ether used was changed to 0.0154g (0.088 mmol) and the amount of benzaldehyde used was changed to 1.245mg (0.0117 mmol).

(example 7)

A stirrer (diameter: 8mm, length: 40mm, no ring) was placed in the center of a stainless steel barrel (outer dimension of opening: 210 mm. times.170 mm, inner dimension of bottom: 170. times.130 mm, height: 30mm) having an inner surface coated with a fluororesin. 340.0g of a partially neutralized solution of sodium acrylate (monomer for polymerization, monomer concentration: 45 mass%, neutralization rate of sodium acrylate: 75 mol%), 0.0541g of ethylene glycol diglycidyl ether (internal crosslinking agent, 0.311 mmol), 1.245mg of benzaldehyde (0.0117 mmol) and 59.0g of ion-exchanged water were added, and then the mixture was uniformly mixed by rotating the stirrer, thereby obtaining a mixture (concentration of partially neutralized solution of sodium acrylate: 38 mass%). Then, the inside of the stainless steel tub was sealed by sealing the upper portion of the stainless steel tub with a polyethylene film. After the temperature of the mixture in the stainless steel barrel was adjusted to 25 ℃, the dissolved oxygen content was adjusted to 0.1ppm or less by replacing the mixture with nitrogen. Subsequently, 3.09g of a 2 mass% V-50 aqueous solution (2, 2' -azobis (2-amidinopropane) dihydrochloride, 0.228 mmol, manufactured by Wako Pure Chemical Industries, Ltd.), 0.65g of a 0.5 mass% L-ascorbic acid aqueous solution and 0.72g of 0.35 mass% hydrogen peroxide were successively added dropwise with stirring at 300rpm, thereby preparing an aqueous monomer solution. Polymerization was started immediately after dropwise addition of 0.35 mass% hydrogen peroxide. After 12 minutes from the start of the polymerization, the obtained product was directly placed in a vessel and immersed in a water bath at 75 ℃ for 20 minutes to be aged, thereby obtaining a gel (gel after polymerization). The thickness of the gel was 1.3 cm. The same operation was carried out to obtain two gels, gel a for making crosslinked polymer particles and gel B for carrying out the cutting test.

Comparative example 1

A gel was obtained by performing the same operation as in example 1, except that benzaldehyde was not used.

Comparative example 2

A gel was obtained by performing the same operation as in example 1 except that the amount of ethylene glycol diglycidyl ether used was changed to 0.0154g (0.088 mmol) and benzaldehyde was not added.

Comparative example 3

A gel was obtained by performing the same operation as in example 7, except that benzaldehyde was not used.

< preparation of crosslinked Polymer particles >

The gels a of the respective examples and comparative examples were treated in the following manner, to obtain respective crosslinked polymer particles.

8 gels were obtained from gel A using scissors, which had a rectangular parallelepiped shape with a width of 2cm, a length of 13cm and a thickness of 1.3 cm. The gel in the shape of a rectangular parallelepiped was sequentially put into a meat chopper (model: 12VR-750SDX, manufactured by Kiren Royal co., ltd.). The diameter of the holes (circular) of the plate located at the discharge opening of the meat grinder was 6.4mm and the density of the holes was 40 holes/36.30 cm². Coarse crushing is carried out until no coarse material (coarsely crushed gel) is discharged from the plate of the meat mincer.

After spreading the coarsely crushed matter on a net, it was dried for 30 minutes by using a hot air dryer (model: FV-320, manufactured by ADVANTEC Co., Ltd.) set to 180 ℃, thereby obtaining a dried matter.

The dried material was pulverized using a pulverizer (Retsch, Rotor Beater Mill, SR300) under conditions such that the sieve has a trapezoidal pore of 1 mm.

The crushed particles were classified by a sieve having a pore size of 850 μm and a sieve having a pore size of 180 μm, and crosslinked polymer particles which passed through the 850 μm sieve and remained on the 180 μm sieve were recovered.

< measurement of CRC >

CRC of crosslinked polymer particles was determined by the following procedure with reference to the EDANA method (NWSP 241.0.R2(15), pp 769-778).

A nonwoven fabric (product name: Heat Pac MWA-18, NIPPON PAPER PAPYLIA CO., LTD. manufactured) having a size of 60mm × 170mm was folded in half along the length direction, thereby being adjusted to a size of 60mm × 85 mm. Nonwoven fabrics were bonded to each other at both sides extending in the longitudinal direction by heat sealing, thereby producing nonwoven fabric bags of 60mm × 85mm (bonded portions of 5mm in width were formed at both sides in the longitudinal direction). 0.2g of the above-mentioned crosslinked polymer particles were contained in the interior of a nonwoven fabric bag. Then, the remaining one side extending in the width direction is pressed by heat sealing, thereby closing the nonwoven fabric bag.

The nonwoven fabric bag was floated on 1000g of physiological saline contained in a stainless steel tank (240 mm. times.320 mm. times.45 mm) in an unfolded state, thereby completely wetting the entire nonwoven fabric bag. After the nonwoven fabric bag was put into physiological saline for 1 minute, the nonwoven fabric bag was immersed in physiological saline with a spatula, thereby obtaining a nonwoven fabric bag containing a gel.

After 30 minutes from the introduction of the nonwoven fabric bag into the physiological saline (total of the floating time of 1 minute and the dipping time of 29 minutes), the nonwoven fabric bag was taken out from the physiological saline. Then, the nonwoven fabric bag was put into a centrifuge (manufactured by KOKUSN Co. Ltd., model: H-122). After the centrifugal force in the centrifugal separator reached 250G, the nonwoven fabric bag was dehydrated for 3 minutes. After dewatering, the mass M of the nonwoven cloth bag including the mass of the gel was weighed_a. The same operation as described above was carried out on the nonwoven fabric bag without housing the crosslinked polymer particles, and the mass M of the nonwoven fabric bag was measured_b. The CRC is calculated according to the following formula. M_cThe mass of the crosslinked polymer particles used for the measurement, i.e., 0.2 g.

The results are shown in Table 1.

CRC[g/g]＝{(M_a－M_b)－M_c}/M_c

< cutting test >

The gels B of the examples and comparative examples were processed in the following manner, and respective cutting tests were performed.

6 test pieces in the form of rectangular parallelepiped 2cm in width, 13cm in length and 1.3cm in thickness were obtained from gel B using scissors. Since voids are easily formed in the region where the stirrers are present in gel B (near the center of the gel), a test piece was obtained from a region where no voids were formed.

The cutting test was carried out using EZTest (product name: EZTest, model: EZ-SX, manufactured by Shimadzu corporation). The jig was assembled by attaching a blade (a long cutting blade, the name of which is described in the product manual: 45 ° cut end surface t3mm) for cutting the gel to a load cell having a capacity of 500N (the upper limit of measurement is set to 450N) with the tip of the blade facing downward in the vertical direction. The blade has a blade head portion (a blade head portion having a length in the direction of the tip of 3mm, gradually narrowing toward the tip, and having a sharp tip) and a plate-like support portion supporting the blade head portion. The length of the cutting blade including the blade head portion in the longitudinal direction was 7 cm. The cutter head part is formed on the whole edge of the supporting part, and the width of one end of the base of the cutter head part and the supporting part is 3 mm. The cutter head portion has: the first blade face inclines from one surface of the supporting part to the front end direction, and the second blade face inclines from the other surface of the supporting part to the front end direction. The first rake face and the second rake face are each inclined 22.5 ° with respect to the tip direction, and the angle (inner angle) between the first rake face and the second rake face is 45 °. The section shape of the knife head part vertical to the length direction is an isosceles triangle.

The test piece was cut by using the Shimadzu test software TRAPEZIUM X (manufactured by Shimadzu Corporation) by the following procedure with a blade mounted to EZTest. The cleavage is carried out at room temperature (25. + -. 1 ℃).

The test piece was placed on the measuring table in a state where the 2cm × 13cm surface of the test piece was in contact with the measuring table and the longitudinal direction of the test piece was orthogonal to the longitudinal direction of the blade. The blade is lowered manually and stopped when the load sensor senses a load of 0.01N. Then, the blade was raised by 0.01mm, and this position was set as a measurement starting point.

The blade was pressed into the surface of the test piece from the measurement starting point at a speed of 20 mm/min (set to automatically operate by the program function of TRAPEZIUM X), and the load applied to the jig when the gel was cut was measured. Fig. 2 is a graph for explaining the test contents of the cutting test, and shows a load-displacement curve of the dependence of the load applied to the jig on the displacement of the jig. As the load increases as the blade is pressed into the gel, the load sharply rises and then sharply falls when the gel is cut, and a peak is observed (refer to (a) of fig. 2), and the load at the peak top P is obtained. When the test piece was not cut, the load reached 450N, which is the upper limit of the measurement (see fig. 2 (b)).

The load (peak load) when each of the 6 test pieces was cut was measured, and the average value of the load (cutting force) was calculated. The results of the cutting test (average value of the load) are shown in table 1. In the examples and comparative examples, all the loads (6 peak loads) were not more than 450N.

[ Table 1]

As is apparent from Table 1, when the CRC of the crosslinked polymer particles is 60g/g or more, a crosslinked polymer gel which can be easily cut can be effectively obtained by using a monomer composition containing a (meth) acrylic acid compound and benzaldehyde.

Description of the reference numerals

10: absorbent body, 10 a: water-absorbent resin particles, 10 b: fiber layers, 20a, 20 b: chip-in-chip, 30: liquid-permeable sheet, 40: liquid-impermeable sheet, 100-absorbent article.

Claims

1. A method for producing a crosslinked polymer gel, which comprises a step of obtaining a crosslinked polymer gel by polymerizing a monomer composition containing benzaldehyde and at least one (meth) acrylic acid compound selected from the group consisting of (meth) acrylic acid and a salt thereof,

the crosslinked polymer gel is coarsely crushed, dried and crushed to obtain crosslinked polymer particles having a centrifuge retention capacity of 60g/g or more.

2. The method for producing a crosslinked polymer gel according to claim 1,

the benzaldehyde content is 0.1 mmol or more based on 1 mol of the (meth) acrylic acid compound.

3. A method for producing crosslinked polymer particles, wherein,

the crosslinked polymer gel obtained by the method for producing a crosslinked polymer gel according to claim 1 or 2 is coarsely crushed, dried and pulverized to obtain crosslinked polymer particles.

4. A monomer composition for obtaining a crosslinked polymer gel, wherein,

the monomer composition contains at least one (meth) acrylic acid compound selected from the group consisting of (meth) acrylic acid and a salt thereof and benzaldehyde,

5. The monomer composition according to claim 4,

6. A crosslinked polymer gel having structural units derived from the monomer composition of claim 4 or 5.